V. Michopoulos, G. Oikonomou, I. Phillips, L. Guan, "CADC: Congestion Aware Duty Cycle Mechanism A Simulation Evaluation", in Proc. 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), 2014
In WSNs idle listening is a major source of energy consumption. Devices can maximise battery, and hence network, lifetime by keeping their radio transceivers off when not needed. We propose CADC, a new Congestion Aware Duty Cycle (DC) MAC protocol, for 6LoWPANs. This protocol uses a new mechanism for the adaptation of the Radio Duty Cycle (RDC), that reacts quickly to changing traffic loads and pat- terns. CADC is independent of network topology, operating protocols and applications and does not require any clock synchronisation between the nodes. Through simulation, we highlight that in static duty cycle MACs there is always a trade-off between energy-efficiency and performance leading to increased energy consumption and low throughput in certain networks. Additionally, it is shown that dynamic protocols can overcome the constraints observed in static DC MACs. CADC outperforms other previously proposed static and dynamic duty cycle protocols in terms of energy consumption, packet loss and goodput while it achieves competitive delay times
T. Butt, I. Phillips, L. Guan, G. Oikonomou, "Adaptive and Context-aware Service Discovery for the Internet of Things", in Proc. 6th conference on Internet of Things and Smart Spaces (ruSMART 2013), St.Petersburg, Russia, pp. 36-47, 2013
The Internet of Things (IoT) vision foresees a future Internet encompassing the realm of smart physical objects, which offer hosted functionality as services. The role of service discovery is crucial when providing application-level, end-to-end integration. In this paper, we propose trendy: a RESTful web services based Service Discovery protocol to tackle the challenges posed by constrained domains while offering the required interoperability. It provides a service selection technique to offer the appropriate service to the user application depending on the available context information of user and services. Furthermore, it employs a demand-based adaptive timer and caching mechanism to reduce the communication overhead and to decrease the service invocation delay. trendy’s grouping technique creates location-based teams of nodes to offer service composition. Our simulation results show that the employed techniques reduce the control packet overhead, service invocation delay and energy consumption. In addition, the grouping technique provides the foundation for group-based service mash-ups and localises control traffic to improve scalability.
W. Rukpakavong, I. Phillips, L. Guan, G. Oikonomou, "RPL Router Discovery for Supporting Energy-Efficient Transmission in Single-hop 6LoWPAN", in Proc. 3rd Workshop On Energy Efficiency in Wireless Networks and Wireless Networks for Energy Efficiency (E2Nets), Ottawa, Canada, pp. 7264-7268, 2012
In Wireless Sensor Networks (WSNs), controlling transmission power is a commonly used technique to extend battery life. This paper describes a novel mechanism using measured RSS (Received Signal Strength) to calculate optimal transmission power. This technique works in multipath environments and with nodes with differing transmission capability. Our technique achieves automatic configuration employing modifications to RPL (Routing Protocol for Low-power and lossy networks) router discovery without requiring extra steps or messages. Consequently, each node can send packets with ideal transmission power, which will usually be lower than maximum power and will help to prolong its lifetime. We evaluate the effectiveness of the proposed scheme, using performance metrics such as energy consumption and packet loss, on an WSN testbed. Several factors that impact the RSS, such as antenna, multipath environment, output power and the node's capabilities are also investigated. Moreover, two RSS estimation techniques are evaluated and compared to the average measured RSS. The experimental results show that energy consumption is reduced by using the proposed technique.
T. Butt, I. Phillips, L. Guan, G. Oikonomou, "TRENDY: An Adaptive and Context-Aware Service Discovery Protocol for 6LoWPANs", in Proc. Third International Workshop on the Web of Things (WoT 2012), Newcastle, UK, pp. 2:1-2:6, 2012
We propose, TRENDY, a new registry-based Service Discovery protocol with context awareness. It uses CoAP-based RESTful web services to provide a standard interoperable interface which can be easily translated from HTTP. In addition, TRENDY introduces an adaptive timer and grouping mechanism to minimise control overhead and energy consumption. TRENDY's grouping is based on location tags to localise status maintenance traffic and to compose and offer new group based services. Our simulation results show that TRENDY techniques reduce the control traffic considerably and also reduce the energy consumption, while offering the optimal service selection.
V. Michopoulos, L. Guan, G. Oikonomou, I. Phillips, "DCCC6: Duty Cycle-Aware Congestion Control for 6LoWPAN Networks", in Proc. 2012 IEEE International Conference on Pervasive Computing and Communications Workshops (PERCOM Workshops), Lugano, Switzerland, pp. 278-283, 2012
In Wireless Sensor Networks (WSNs), congestion can cause a number of problems including packet loss, lower throughput and poor energy efficiency. These problems can potentially result in reduced deployment lifetime and under-performing applications. This has led to several proposals for congestion control (CC) mechanisms for sensor networks. Furthermore, the WSN research community has made significant efforts towards power saving MAC protocols with Radio Duty Cycling (RDC). However, careful study of previous work reveals that RDC schemes are often neglected during the design and evaluation of CC algorithms. In this context, this paper contributes a new CC scheme for Duty Cycle and IPv6 over Low power Wireless Personal Area Networks 6LoWPAN sensor Networks - DCCC6. DCCC6 detects the presence of duty cycling and adjust its operation accordingly. We evaluate DCCC6 both with simulations and on a testbed with multi node topologies. The experimental results have shown that DCCC6 achieved higher goodput and lower packet loss than previous works. Moreover, simulations show that DCCC6 maintained low energy consumption, average delay times and achieved a high degree of fairness.
V. Michopoulos, L. Guan, G. Oikonomou, I. Phillips, "A Comparative Study of Congestion Control Algorithms in IPv6 Wireless Sensor Networks", in Proc. 2011 International Conference on Distributed Computing in Sensor Systems and Workshops (DCOSS), Barcelona, Spain, pp. 1-6, 2011
In Wireless Sensor Networks (WSNs), congestion can cause a plethora of malfunctions such as packet loss, lower throughput and energy inefficiency, potentially resulting in reduced deployment lifetime and under-performing applications. This has led to several proposals describing congestion control (CC) mechanisms for sensor networks. Furthermore, the WSN research community has made significant efforts towards power saving MAC protocols with Radio Duty Cycling (RDC). However, careful study of previous work reveals that RDC schemes are often neglected during the design and evaluation of congestion control algorithms. In this paper, we argue that the presence (or lack) of RDC can drastically influence the performance of congestion detection. In addition, most WSN CC mechanisms are evaluated under traditional sensor network topologies and protocols (e.g. trickle data dissemination, tree data collection). The emerging IPv6 over Low power Wireless Personal Area Networks (6LoWPAN) and related standards pose a new requirement: we now need to investigate if previous findings regarding congestion control are still applicable. In this context, this paper contributes a comprehensive evaluation of existing congestion detection mechanisms in a simulated, multi-node 6LoWPAN sensor network. We present results from two sets of experiments, differentiated by the presence or lack of RDC.
G. Oikonomou, I. Phillips, L. Guan, A. Grigg, "ADDER: Probabilistic, Application Layer Service Discovery for MANETs and Hybrid Wired-Wireless Networks", in Proc. 9th Annual Communication Networks and Services Research Conference (CNSR 2011), Ottawa, Canada, pp. 33-40, 2011
Over the past years, Mobile ad-hoc networks (MANETs) have attracted a considerable degree of research attention, with service discovery, selection and invocation being among the topics of interest of previous efforts. In this paper we introduce ADDER, a probabilistic, hybrid, directory-less service discovery mechanism. It has been designed for military IPv6-based MANETs but will work in any hybrid wired-wireless deployment. It achieves very low service acquisition time through the exchange of a very small number of short messages. Propagation of service descriptions is based on a distance vector algorithm, achieving loop and starvation freedom through a feasibility condition, which has been adopted from established and well-tested routing protocols. This paper also presents evaluation results, obtained by actual execution of the ADDER daemon on two different test beds. The experiments aim to demonstrate that the mechanism achieves good scalability with increasing number of services and network size.
T. Edwan, L. Guan, G. Oikonomou, I. Phillips, "Higher Order Delay Functions for Delay-Loss Based TCP Congestion Control", in Proc. 6th Wireless Advanced, London, UK, pp. 1-6, 2010
TCP-Illinois aims to address TCP's low throughput when operating in high-speed, high-delay networks. Previous research has shown that, due to its linear increase behaviour and to its relatively long congestion epochs, TCP-Illinois exhibits sub-optimal scaling behaviour with an increasing path Bandwidth-Delay Product (BDP). This paper discloses our contributions towards improving the aggressiveness and responsiveness of loss-based TCP congestion control algorithms. We formally show that higher order versions (of power n) of the delay functions used by TCP-Illinois become more aggressive and responsive with an increasing value of n. Based on this finding, we propose three variants: i) a second order (quadratic) version of additive increase and multiplicative decrease (TCP-Q), ii) a second order multiplicative decrease only (TCP-Fq) and iii) a sub-linear multiplicative decrease only (TCP-Fs). By modifying the TCP-Illinois code in the GNU/Linux kernel, we obtained the three corresponding modules and used them for our simulations using the TCP/Linux patch for ns2. Based on standardised congestion control metrics, we conducted a comparative analysis between our variants and a number of relevant high speed TCP algorithms. Simulation results agree with our analytical findings; compared to TCP-Illinois, TCP-Q exhibits shorter congestion epochs and thus better responsiveness and convergence.
T. Edwan, L. Guan, G. Oikonomou, I. Phillips, "Understanding the Impact of Link Errors on TCP Congestion Control", in Proc. 26th UK Performance Engineering Workshop (UK PEW 2010), Coventry, UK, pp. 59-64, 2010
This paper presents a control-theoretic-like analysis of TCP congestion control mechanism. We extend previous analysis by considering two additional factors: i) wireless link errors and ii) general variable multiplicative decrease (MD). Wireless link errors are usually the cause for unnecessary TCP congestion window reductions and thus lower throughput. We also study the effects of those parameters on TCP's stability condition. In this paper, we present a modified TCP model and analyse it in the presence of delay. This is then linearised around an equilibrium point and re-analysed using a control-theoretic-like framework. The analysis verifies that non-congestive packet loss acts as a disturbance, as opposed to loss due to congestion, which is well within TCP's control.
G. Oikonomou, I. Phillips, L. Guan, A. Grigg, "An Emulator for the Network Stack of Integrated Modular Systems", in Proc. 5th IEEE International Conference on Systems of Systems Engineering (IEEE SoSE), Loughborough, UK, 2010
The networked integration of military systems can enable timely exploitation of intelligence and offer strategic advantages in the battlefield. Despite operating under harsh, hostile conditions, tactical networks have many similarities with typical wireless ad-hoc networks. The UK Ministry of Defence Standard 00-74 attempts to standardise an architecture for integrated avionics and includes the specification of a three layer network stack for the message exchange between applications on board a system. As part of our work, we developed an emulator for this network stack. Furthermore, we have designed and implemented a service discovery mechanism for mobile ad hoc networks. This paper focuses on disclosing the emulator's design and implementation details. We also discuss the emulator's integration with the service discovery mechanism in order to achieve scalable, reconfigurable off board communications towards IPv6 based systems of systems.
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